RFID verifier system with grade classification

ABSTRACT

An RFID verifier includes a transmit signal strength indicator (TSSI) and a receive signal strength indicator (RSSI). Using the TSSI, the RFID verifier may determine the amount of power an interrogated RFID tag is illuminated with. Similarly, using the RSSI, the RFID verifier may determine the amount of power returned to the RFID verifier by the RFID tag. By processing the returned power and the illuminating power with a transfer function, the RFID verifier may provide an absolute indicia of quality for the interrogated RFID tag.

FIELD OF INVENTION

The present invention relates generally to RFID applications. Moreparticularly, the present invention relates to an RFID reader orinterrogator configured to, verify RFID transponder operation.

BACKGROUND

Radio Frequency Identification (RFID) systems represent the next step inautomatic identification techniques started by the familiar bar codeschemes. Whereas bar code systems require line-of-sight (LOS) contactbetween a scanner and the bar code being identified, RFID techniques donot require LOS contact. This is a critical distinction because bar codesystems often need manual intervention to ensure LOS contact between abar code label and the bar code scanner. In sharp contrast, RFID systemseliminate the need for manual alignment between an RFID tag and an RFIDreader or interrogator, thereby keeping labor costs at a minimum. Inaddition, bar code labels can become soiled in transit, rendering themunreadable. Because RFID tags are read using RF transmissions instead ofoptical transmissions, such soiling need not render RFID tagsunreadable. Moreover, RFID tags may be written to in write-once orwrite-many fashions whereas once a bar code label has been printedfurther modifications are impossible. These advantages of RFID systemshave resulted in the rapid growth of this technology despite the highercosts of RFID tags as compared to a printed bar code label.

Although RFID systems have certain advantages over bar coding schemes,they share many concerns as well. For example, bar code scanners canmerely read a bar code label; they cannot provide a measure of quality.Because a marginal bar code may be readable by one scanner but notanother, users have no way of reliably detecting the marginal bar codesusing conventional bar code scanners. Thus, bar code verifiers have beenused to measure bar code quality metrics such as contrast, average bardeviation, and related quality indicia. Marginal bar code labels maythus be identified by bar code verifiers, thereby assuring users thattheir products may be reliably identified. The same concern for qualityapplies to RFID tags as well. However, the backscatter modulationcommonly used to read information from passive RFID tags complicates theRFID verification process. In backscatter modulation, the interrogatingRF beam itself provides the power for the RFID tag to respond. Oneverification metric would thus be how well a given RFID tag absorbed RFenergy and retransmitted the energy to the RFID reader. But RF energy isabsorbed by many objects in an RFID tag's environment. A conventionalRFID reader has no way of determining whether a tag has absorbed RFenergy or whether the absorption occurred due to environmental effects.Instead, a conventional RFID reader can merely determine thesignal-to-noise ratio (SNR) of the backscattered signal from a passiveRFID tag. A marginal RFID tag may be malfunctioning but illuminated withenough RF energy that the backscattered signal provided a sufficient SNRso that the RFID tag's signal may be decoded correctly. This samemarginal RFID tag may be unreadable in less pristine RF environments. Ifan RFID tag could be verified to a known standard, such marginal RFIDtags could be detected and replaced.

The need to verify RFID tags to a known standard is exacerbated by otherRFID system properties. For example, RFID tags are notwhat-you-see-is-what-you-get (WYSIWYG) whereas a bar code label is. Inother words, it doesn't matter what type of article a bar code label isaffixed to because readability of the label is not affected, forexample, by the article's color. However, the readability of an RFID tagmay be strongly affected by the environment in which it is located.Thus, it is not possible to create a golden standard without knowledgeof an RFID tag's context or environment. Moreover, because RFID tags canbe physically or electrically damaged in transit, RFID systems arecomplicated by the need to find a safe position for the RFID tag. Thejuggling of RFID tag placement with RF absorption from the tag'senvironment can be a formidable task. Finally, the programmability ofRFID tags requires that the fidelity of the RF link between an RFIDreader and the RFID tag being interrogated must be relatively flawless.Accordingly, there is a need in the art to provide an RFID verifier thatcan more accurately verify operation of RFID tags usingcontext-sensitive quality standards.

SUMMARY

In accordance with one aspect of the invention, an RFID verifier isprovided. The RFID verifier includes: a transceiver operable tointerrogate with an interrogating signal an RFID tag and to read aresulting signal from the interrogated RFID tag; a transmit signalstrength indicator operable to measure the interrogating signal power; areceived signal strength indicator operable to measure the power of thesignal from the interrogated RFID tag; and a processor operable tocompare the measured interrogating signal power and RFID tag signalpower to obtain an measure of quality for the interrogated RFID tag, theprocessor being configured to classify the measure of quality withreference to a predetermined absolute measure of quality.Advantageously, this RFID verifier allows the user to createcontext-sensitive standards. Should the RFID verifier be integrated witha bar code printer, the RFID verifier may use these context-sensitivestandards to allow only standard-passing tags to have a bar code labelprinted without backup and over-striking of the RFID tag.

In accordance with another aspect of the invention, an RFID tagverification method is provided that includes the acts of: determining afirst location from which an absolute measure of quality may be measuredfrom a first RFID tag; from a second location: determining a measure ofquality for the first RFID tag to establish a transfer function betweenthe measure of quality at the second location and the absolute measureof quality from the first location; interrogating a second RFID tag withan interrogating RFID signal; measuring the power of the interrogatingRF signal; receiving a modulated RF signal from a second interrogatedRFID tag; measuring the power of the received modulated RF signal fromthe second interrogated RFID tag; and processing the measured powersfrom the interrogated second RFID tag with the transfer function toprovide an absolute measure of quality for the interrogated second RFIDtag. Based upon the absolute measure of quality, the interrogated secondRFID tag may then be classified as either accepted or rejected.

In accordance with another aspect of the invention, a system is providedthat includes: a bar code label printer; and an RFID verifier includinga transceiver operable to interrogate with an interrogating signal anRFID tag and to receive a resulting backscattered signal from theinterrogated RFID tag; a transmit signal strength indicator operable tomeasure the interrogating signal power; a received signal strengthindicator operable to measure the signal power from the interrogatedRFID tag; and a processor operable to compare the measured interrogatingsignal power and RFID tag signal power to obtain an measure of qualityfor the interrogated RFID tag, the processor being configured toclassify the measure of quality with reference to a predeterminedabsolute measure of quality, wherein the interrogated RFID tag isassociated with an article, the system being configured to apply a barcode label from the printer to the article if the measure of quality isclassified into an acceptable grade of quality.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an RFID verifier in accordance with anembodiment of the invention.

FIG. 2 is a schematic illustration of an RF transceiver for the RFIDverifier of FIG. 1.

FIG. 3 is illustrates an RFID tag antenna emission pattern with respectto an azimuth scan by an RFID verifier in accordance with an aspect ofthe invention.

FIG. 4 is a graph of the signal intensity as a function of range.

FIG. 5 illustrates a verifier display having fiducials oriented suchthat the verifier may be located at a predetermined angular displacementfrom the RFID tag antenna boresight.

FIG. 6 illustrates the verifier display of FIG. 5 having the fiducialsoriented such that the verifier may be located at another predeterminedangular displacement.

FIG. 7 is a graph of the signal strength profile as a function ofangular displacement resulting from a scan between the angulardisplacements of FIGS. 5 and 6.

FIG. 8 is a block diagram of an RFID verifier in accordance with anembodiment of the invention.

FIG. 9 illustrates a system having a verifier integrated with a bar codeprinter in accordance with an embodiment of the invention.

FIG. 10 illustrates the beam intensity patterns for RFID tags havingeither a bowtie patch antenna or a dipole antenna.

DETAILED DESCRIPTION

Turning now to the Figures, a block diagram of an exemplary RFIDverifier 100 is shown in FIG. 1. RFID verifier 100 includes an RFtransceiver and processor 105. As known in the RFID art, transceivertransmits an RF signal 110 to provide power to a passive RFID tag 120.Having thus been provided energy, passive RFID tag modulates the RFsignal 110 and backscatters an encoded RFID signal 125 to RF transceiver105. Transceiver 105 includes separate RF antennas 130, one fortransmitting RF signal 110 and another for receiving encoded RFID signal125. However, it will be appreciated that other embodiments of RFtransceiver 105 could use a single antenna for both transmission andreception.

During verification, it is desirable that RFID verifier 100 be locatedin an optimum location for interrogating RFID tag. For example, RFID tag120 may include a dipole antenna having a maximum gain in a boresightdirection 140. To get a measure of the quality for RFID tag 120,verifier 100 should be located such that the maximum gains of antennas130 are also in the boresight direction 140. If verifier 100 is notoptimally oriented in this fashion, an otherwise acceptable RFID tag 120may be deemed of low quality simply because antennas 120 and 130 are notoriented to transmit and receive the maximum achievable RF energy. Ananalogous orientation must be made during verification of bar codelabels in that if the bar code verifier is not normally directed to thebar code label, the resulting skew affects the quality of the bar codedecryption. It will be appreciated that RFID tag 120 could be providedwith fiducials such that a trained technician would understand how tomanually orient RFID verifier 105 in the optimal orientation withrespect to the tag's fiducials.

To eliminate the need for a trained technician who would appreciate, forexample, that if a tag's antenna is a dipole antenna, how to properlyorient RFID verifier 100 with respect to this dipole's boresight,embodiments of RFID verifier 100 will include intelligence to assist anoperator in the proper orientation. For example, RFID verifier 100 mayinclude an image processor 150 coupled to a lens assembly 155 and adisplay 160. Depending upon the desired orientation of verifier 100,image processor 150 would orient fiducials 165 on display 160 such thatan image of RFID tag 120 is centered within these fiducials 165.Alternatively, as will be explained further herein, verifier 100 mayinclude a GPS unit (not illustrated) so as to assist in the properorientation of verifier 100.

To provide an indicia of tag quality, verifier 100 includes a receivedsignal strength indicator (RSSI) 170 and a transmitted signal strengthindicator (TSSI) 175. Rather than use relative indicia such as SNR orbit error rate, RSSI 170 should be configured such that it provides acalibrated indication of the received signal strength. In this fashion,processor 105 may compare transmitted power for RF signal 110 asprovided by TSSI 175 to received power for encoded RFID signal 125. Forexample, based upon this comparison, RFID tags could be sorted into “A”level, “B” level, and “C” level categories. Advantageously, thiscomparison can be made for RFID tags that are on packages in aproduction setting. Marginal RFID tags may then be immediately detectedand replaced as necessary.

Turning now to FIG. 2, a schematic illustration for an exemplaryembodiment of a superheterodyne transceiver 105 is shown. It will beappreciated, however, that baseband or homodyne architectures may alsobe implemented. A low noise amplifier (LNA) 200 amplifies a received RFsignal denoted as RF_(in) (signal 125 in FIG. 1) to provide an input toan RF multiplexer (MUX) 205. After coupling through RF MUX 205, theamplified received RF signal is downconverted to IF in a mixer 210responsive to a local oscillator (LO) signal. The downconverted analogIF signal from mixer 210 may then be digitized in an analog-to-digitalconverter (ADC) 215 to provide a digital IF signal. A digitaltransceiver 250 decodes the digital IF to identify the RF tag beinginterrogated. In addition this decoding may be used to provide otherindicia of quality such as bit error rate (BER).

As discussed in the background section, verification based upon arelative variable for the received RF signal such as SNR would be errorprone because the resulting RFID verifier would have no way ofdistinguishing, for example, an otherwise-acceptable RFID tag locatedwithin an RF absorbing environment from an unacceptable RFID tag locatedin a pristine RF environment. To provide an accurate received signalstrength indication, an LNA 220 matched to LNA 200 amplifies a referencesignal from a reference oscillator 225 to provide an amplified referencesignal to RF MUX 205. Thus, through operation of RF MUX 205, either theamplified reference signal or the amplified received RF signal isdownconverted in mixer 210 and then digitized in ADC 215. Referenceoscillator 225 is calibrated such that if MUX 205 selects for theamplified reference signal, the resulting digitized IF reference signalis also of known power because the gain of LNA 220 is known. In thisfashion, the digitized IF received signal may be compared to a digitizedreference IF signal of known power such that an absolute power value forthe digitized IF received signal may be obtained through the comparison.

An analogous measurement is made for an RF signal (denoted as RF_(out))that will couple to the transmitting antenna 130 (FIG. 1) to providetransmitted RF signal 110. To provide RF_(out), transceiver 100generates a digital IF signal 229 that is converted into analog form ina digital-to-analog converter (DAC) 230. It will be appreciated thatreference oscillator 225 may be formed in an analogous fashion: thegeneration of a reference digital IF signal that is then upconvertedaccording to a reference RF signal. Digital IF signal 229 is upconverted to RF in a mixer 235 responsive to the LO signal. A poweramplifier 240 amplifies the resulting RF signal to provide RF_(out). Itwill be appreciated that transmitting antenna 130 has internal lossessuch that the power of transmitted RF signal 110 is less than the powerin RF_(out). It is desirable, however, to accurately know the power ofthe transmitted RF signal 110 to properly verify an RFID tag. Thus, TSSI175 receives both the input to power amplifier 240 and its output.Because the gain of power amplifier 240 is known, TSSI 175 can thencalculate the power for transmitted RF signal 110, thereby accountingfor any losses introduced by transmitting antenna 130.

It will be appreciated that numerous processing architectures may beused to process the received digital IF signal and to generate thetransmitted digital IF signal. For example, transceiver 250 includingdigital filters, I/Q demodulators, and a digital signal processor may beused to process and generate these signals. Higher-level functions wouldbe implemented within a microprocessor 260. An input/output and userinterface module 270 allows a user to interact with microprocessor 260.Regardless of the particular architecture implemented, the use of RSSI170 and TSSI 175 enables an accurate verification of RFID tags.

Prior to verification of an RFID tag, the optimum range between the tagand verifier 100 should be determined. This optimal range may beexperimentally determined or be provided by the manufacturer of the RFIDtag being verified. A user of verifier 100 may perform an experimentaldetermination by making received signal strength measurements at varyingranges in the boresight direction 120 for RFID tag 120.

These range-varying measurements may be better explained with respect toa typical antenna emission pattern for an RFID tag dipole antenna isshown in FIG. 3. As can be seen from the emission pattern, transmittedRF energy from the antenna drops off as angular displacements are madefrom boresight direction 140, which is denoted as the ideal read path inFIG. 3. For example, measurements made at the angular displacementsdenoted as azimuth 1 and azimuth 2 will mischaracterize the transmittedsignal strength. However, measurements made in the boresight direction140 will measure the strongest emissions from the RFID antenna. Anexemplary graph of measurements made along boresight direction 140 isshown in FIG. 4. It can be seen that transmitted signal strength fromthe RFID tag peaks at an ideal read position A. Should measurementsoccur any closer to RFID tag 120 than position A, near-field effectsdecrease the transmitted signal strength. Similarly, should measurementsoccur at ranges further than position A from RFID tag 120, far-fieldeffects decrease the transmitted signal strength. A typical range forideal read position A is approximately three meters. However, it will beappreciated that an ideal read position for a given RFID tag will dependupon the type of antenna being implemented within the given RFID tag.

Having determined the ideal read position, the corresponding range fromRFID tag 120 to verifier 100 may be used to size fiducials 165 such thata user may readily manually orient verifier 100 at the proper range byaligning fiducials 165 with RFID tag 120. It will be appreciated thatverifier 100 may be configured with varying sets of fiducials 165corresponding to varying types of RFID tags being verified. Dependingupon the particular RFID tag being verified, a user could, for example,select from a pull down menu the appropriate fidicials 165.

Having been configured with the appropriate fiducials 165, a user maymanually locate verifier 100 such that RFID tag 120 is centered withinfiducials 165, thereby assuring that verifier 100 is located at therange of the ideal read position A from RFID tag 120. By introducing theappropriate skew to fiducials 165, a desired angular displacement fromboresight direction 140 may be achieved. It will be appreciated that thealignment of fiducials 165 is with respect to RFID tag physicallandmarks such as the tag outline. If the RFID tag antenna is assumed tobe aligned in a precise fashion with the tag physical landmarks, thenthe alignment of fiducials 165 with the physical landmarks of the RFIDtag produces a corresponding alignment with the RFID tag antenna. Insuch a case, fiducials 165 may be oriented such that by aligning themwith the physical landmarks of the RFID tag being verified, a user willlocate verifier 100 at the ideal read position A. However, the alignmentof an RFID tag antenna may be skewed or unknown with respect to thephysical landmarks. In such a case, verifier 100 may be configured tolocate fiducials 165 within display 160 such that a user will scanacross the transmitted RF beam from RFID tag 120 to find the maximumantenna gain direction 140. Verifier 100 may then locate fiducials 165appropriately so that a user will align verifier 100 in the maximumantenna gain direction 140. Because the ideal range has already beenpredetermined and accounted for in the dimensions of fiducials 165,verifier 100 will then be at the ideal read position A discussed withrespect to FIG. 3.

This scanning procedure may be better understood with reference to FIGS.5 and 6. FIG. 5 shows an exemplary arrangement of fiducials 165 withindisplay 160 such that when RFID tag physical landmarks 500 are alignedwithin fiducials 165, verifier 100 is offset from the maximum antennagain direction 140. For example, fiducials 165 may be arranged such thatverifier 100 is displaced to read position azimuth 1 as shown in FIG. 3.After the received signal strength is measured at read position azimuth1, fiducials 165 may be aligned within display 160 as seen in FIG. 6such that a user will be forced to scan across the antenna beam toanother read position such as the read position for azimuth 2 in FIG. 3.As the user scans across the antenna beam, the verifier 100 continues tosample the antenna beam to measure received signal strength. In thisfashion, a profile of the received signal strength may be expected asseen in FIG. 7. To form this profile, verifier 100 may monitor thelocation of the physical landmarks 500 within display 160 as the time ofeach measurement. For example, if a user scans slowly in a first portionof the scan and then scans more rapidly in a second portion of the scan,the profile should reflect that the measurement points within the firstportion are more closely spaced than the measurement points in thesecond portion of the scan. By correlating the time of each measurementswith the position of physical landmarks 500 within display 160 at eachmeasurement time, each measurement may be located at the correct angulardisplacement as seen in FIG. 7. Verifier 100 may then analyze theprofile to determine the maximum antenna gain direction 140. Havinglocated maximum antenna gain direction 140, verifier may locatefiducials 165 within display 160 such that a user will be positionverifier 100 at the ideal read position A. Verification of RFID tag 120may then proceed as discussed herein.

In an alternative embodiment, rather than employ a visual orientationapproach as just discussed, verifier 100 may be configured with a globalpositioning system (GPS) 800 as seen in FIG. 8. To perform an antennabeam scan, a user may first measure the coordinates of RFID tag 120.Knowing these coordinates, verifier 100 may then calculate thecoordinates of the read position at azimuth 1 and 2 as discussed withrespect to FIG. 3. The user would be instructed to move verifier 100accordingly such that it scans across the antenna beam to form a profileas discussed with respect to FIG. 7.

Regardless of how the ideal read position discussed with respect to FIG.3 is determined, a verifier may then be located at this ideal position.This is akin to locating a bar code label verifier normally with respectto the bar code label surface. It will be appreciated that having foundthe ideal read position, the verifier being located at this ideal readposition need not be configured to include any imaging capability asdiscussed with respect to FIGS. 5, 6, and 7. Instead, a verifier thatmerely possesses the TSSI and RSSI capabilities discussed with respectto FIG. 2 is sufficient. But because this verifier is located at theoptimal read position, the measure of quality it determines for theinterrogated RFID tag is an absolute measure of quality for theinterrogated tag. In other words, the absolute measure of quality is notaffected by variables such as being located off-beam from theinterrogated RFID tag. This absolute measure of quality may then be usedas follows to classify RFID tags.

In a production environment, it will often not be possible or practicalto mount a verifier at the optimal read location. In such environments,the verifier must often be located at a sub-optimal location such themeasure of quality it obtains from interrogated RFID tags is affected byvariables such as being located off-beam. With no other knowledge of itsrelationship to the optimal read location, the sub-optimally-locatedRFID verifier would have no way of knowing whether the interrogated RFIDtag was providing a weak signal because the tag itself was defective orwhether the interrogated RFID tag was good but simply being interrogatedtoo far off-beam to receive an adequate signal. Embodiments of thepresent invention solve this dilemma by providing an RFID verifier thatknows the relationship between the measure of quality that would beexpected at its current location based upon the absolute measure ofquality obtained at the optimal read location. This relationship may bereferred to as a transfer function.

To obtain the transfer function, an RFID verifier such as RFID 100 ofFIG. 1 may be used to measure, in the production environment, theabsolute measure of quality for the particular type of RFID tag beingverified. A “production” RFID verifier may then be mounted in itsreal-world location. As discussed with respect to subsequent reads oftags from the optimal read location, the production RFID verifier beinglocated at a sub-optimal read location need not be configured to includeany imaging capability as discussed with respect to FIGS. 5, 6, and 7.Instead, a verifier that merely possesses the TSSI and RSSI capabilitiesdiscussed, for example, with respect to FIG. 2 is sufficient. To obtainthe transfer function, the production RFID verifier may interrogate anRFID tag whose absolute level of quality has been verified from theoptimal read location. For example, the absolute level of quality forthe interrogated tag may be an “A” level. However, from the sub-optimallocation, the production RFID verifier measures the same tag to have a“B” level of quality. Thus, for this example, the transfer function issuch that the measure of quality from the sub-optimal location must beincreased by one grade. Advantageously, an absolute level of quality forthe interrogated tags may be determined by the production RFID verifier.

The production RFID verifier may then be integrated or associated with abar code printer. Bar code labels printed by the bar code printersupplement or duplicate RFID tag information as known in the art. Anarticle having an RFID tag would may thus have a bar code label asprinted by the bar code printer. However, because the production RFIDverifier is associated with the bar code printer, articles having RFIDlabels that are not of a suitable quality level may be rejectedimmediately. An exemplary printer/verifier system 900 is shown in FIG.9. Articles having RFID tags 905 are transported sequentially past aproduction RFID verifier 910. Because the production RFID verifier hasbeen configured with the transfer function as just discussed, it mayobtain an absolute measure of tag quality by sequentially reading themas they pass by. As illustrated, an article 920 is the one having itsRFID tag 905 verified. An article 925 has already had its tag verified.Thus, a bar code label 930 from a bar code printer 935 has been appliedto article 925. After article 920 has had its tag verified, an article940 may be transported to the ideal read location, stopped, and have itstag verified, and so on. Those articles whose RFID tags 905 are not ofsuitable quality will be identified so that their RFID tags 905 may bereplaced.

Because production RFID verifier 910 may obtain quality measures fromeach tag as they are sequentially transported past its location, thesequality measures may be used, to reconstruct an antenna beam intensityor gain profile for the tag's antenna analogously as discussed withrespect to FIG. 7. In the production environment, however, the antennascan may not occur through the maximum antenna gain direction 140.However, because the transfer function is known, it is as if productionRFID verifier 910 scans through this direction. It will be appreciatedthat certain types of RFID tags may have the same encoding but usedifferent antennas. For example, one type of RFID tag may use amplitudeshift keying in the same manner to encode its RFID information but beproduced in two or more classes, where the antenna being implementeddistinguishes each class from the remaining classes. Production RFIDverifier 910 may distinguish and identify these classes within the sametype of RFID tag by examining the antenna beam scan. By suchexamination, for instance, a dipole antenna intensity pattern may bedistinguished from a patch antenna intensity pattern. In this fashion,production RFID verifier 910 may sort classes of RFID tags according totheir observed antenna patterns.

The classification of RFID tags with respect to antenna types may bebetter understood with reference to FIG. 10. As seen in FIG. 10, an RFIDtag 1000 having a bowtie patch antenna 1005 and an RFID tag 1110 havinga dipole antenna 1015 are illustrated. RFID tags 1000 and 1110 have thesame encoding and modulation scheme. Thus, a conventional RFID readerwould be unable to distinguish these tags during normal operation.However, production RFID verifier 910 (FIG. 9) determines thecorresponding beam intensity patterns while scanning tags 1000 and 1110as they are transported past production RFID verifier 910. Asillustrated, bowtie patch antenna 1005 produces a significantly narrowerantenna intensity pattern than does dipole antenna 1015. Production RFIDverifier 910 may be configured to store the expected beam intensitypattern as part of the transfer function discussed previously. Bycomparing the measured beam intensity patterns to the stored transferfunctions, production RFID verifier 910 may classify tags according totheir antenna types.

As just described, verifier 910 bases its quality gradations for theverified tags solely upon the RF energy interrogation of the tag beingverified. However, it will be appreciated that these gradations may alsobe affected by other contextual information. For example, a user ofverifier 910 may recognize that a certain class of articles are havingtheir RFID tags verified. Alternatively, this recognition may beautomated through a machine reading of SKU information. Given thiscontextual information, verifier 910 may alter its gradationsaccordingly. For example, whereas the same verified quality for one typeof article may be classified as an “A” grade, this same verified qualityfor another type of article may be classified as a “B” grade. Inaddition, the classification of RFID tags according to their antennatypes may also be influenced by SKU information. For example, one typeof goods may be suitable for wide beam width tags whereas another typeof goods will need tags having a narrower beam.

Consider the advantages of system 900—because the verification of RFIDtags is context dependent, another verifier may be used to determine theworst-case scenario for subsequent verification of articles such asarticle 920 at a different location. For example, system 900 may be usedto verify tags in a production environment. When the articles areshipped to a customer or intermediate location such as a warehouse, auser at these subsequent locations will want to be assured that thepreviously-verified RFID tags 905 are still readable. The transferfunction from the production facility to the customer facility may bemeasured to enable this assurance. For example, the transfer functionmay be such that an “A” level tag at the production facility becomes a“B” level tag in the context of a customer's warehouse. Similarly, a “B”level tag may become a “C” level tag under this transfer function. Ifthe user determines that only “B” level tags are acceptable at itswarehouse, then system 900 at the production facility will only pass “A”level tags given this transfer function.

The classification process described with respect to FIG. 10 may begeneralized and applied to RFID readers/interrogators that do notincorporate TSSI capabilities. Instead an RFID reader need merely beconfigured with knowledge of the expected beam intensity patterns and anRSSI capability. As such an RFID reader scans RFID tags, it maydetermine the beam intensity pattern as discussed with respect to FIG.10. By comparing the measured beam intensity patterns to the expectedbeam intensity patterns for various known antenna types, the RFID readermay classify the scanned RFID tags accordingly. Moreover, such an RFIDreader may be configured to scan at multiple frequencies such as 13.56MHz, 915 MHz, or any other suitable RFID frequency. The RFID reader maythen determine what frequency range the interrogated RFID tag respondedto. In turn, the RFID reader may then identify the modulation protocolbeing implemented in the interrogated tag such as BPSK or ASK. Finally,the RFID reader may then identify the antenna type being implemented inthe interrogated RFID tag as just discussed.

It will be appreciated that numerous modifications may be made to thepreceding description. For example, the scanning process may beautomated. In an automated embodiment, a verifier may be movably locatedon a mechanized positioner. The verifier would control the mechanizedpositioner so that a scan may be performed. Accordingly, although theinvention has been described with respect to particular embodiments,this description is only an example of the invention's application andshould not be taken as a limitation. Consequently, the scope of theinvention is set forth in the following claims.

1. An RFID tag verification method, comprising: determining an optimallocation from which an absolute measure of quality may be measured froma first RFID tag; from a second location: determining a measure ofquality for the first RFID tag to establish a transfer function betweenthe measure of quality at the second location and the absolute measureof quality from the optimal location; interrogating a second RFID tagwith a first interrogating RFID signal; measuring the power of theinterrogating RF signal; receiving a modulated RF signal from a secondinterrogated RFID tag; measuring the power of the received modulated RFsignal from the second interrogated RFID tag; and processing themeasured powers from the interrogated second RFID tag with the transferfunction to provide an absolute measure of quality for the interrogatedsecond RFID tag.
 2. The RFID tag verification method of claim 1, whereindetermining a first location from which an absolute measure of qualitymay be measured from a first RFID tag comprises: from a plurality oflocations, interrogating the first RFID tag with a second interrogatingRFID signal, the second interrogating RFID signal having the same poweras the first interrogating RFID signal; at each of the locations in theplurality of locations, receiving a modulated RF signal from a firstinterrogated RFID tag; measuring the power of the received modulated RFsignal from the first interrogated RFID tag for each of the locations inthe plurality; comparing the measured powers of the received modulatedsignal from the first interrogated RFID tag to determine the greatestpower, wherein the location with the greatest power is the firstlocation.
 3. The method of claim 2, further comprising: classifying thesecond RFID tag based upon its absolute measure of quality.
 4. Themethod of claim 3, wherein the classification comprises classifying thesecond RFID tag into either a passing grade or a failing grade.
 5. Themethod of claim 4, wherein the passing grade comprises a plurality ofpassing grades.
 6. The method of claim 3, wherein the classification ofthe second RFID tag is further based upon additional information.
 7. Themethod of claim 6, wherein the additional information comprises SKUinformation.
 8. A system, comprising: a bar code label printer; and anRFID verifier including: a transceiver operable to interrogate with aninterrogating signal an RFID tag and to receive a resultingbackscattered signal from the interrogated RFID tag; a transmit signalstrength indicator operable to measure the interrogating signal power; areceived signal strength indicator operable to measure the signal powerfrom the interrogated RFID tag; and a processor operable to compare themeasured interrogating signal power and RFID tag signal power to obtainan measure of quality for the interrogated RFID tag, the processor beingconfigured to classify the measure of quality with reference to apredetermined absolute measure of quality, wherein the interrogated RFIDtag is associated with an article, the system being configured to applya bar code label from the printer to the article if the measure ofquality is classified into an acceptable grade of quality.
 9. The systemof claim 8, wherein the classification of the measure of quality is afunction of SKU information from the article.
 10. The system of claim 8,wherein the transceiver is a superheterodyne transceiver.
 11. The systemof claim 8, wherein the transceiver is a homodyne transceiver.
 12. AnRFID tag verification method, comprising: determining an optimallocation from which an absolute measure of quality may be measured froma first RFID tag; from a second location: determining a measure ofquality for the first RFID tag to establish a transfer function betweenthe measure of quality at the second location and the absolute measureof quality from the optimal location; interrogating a second RFID tagwith a first interrogating RFID signal; measuring the power of theinterrogating RF signal; receiving a modulated RF signal from a secondinterrogated RFID tag; measuring the power of the received modulated RFsignal from the second interrogated RFID tag; and processing themeasured powers from the interrogated second RFID tag with the transferfunction to identify an antenna type implemented in the second RFID tag.